Semaphorin 4D induced inhibitory synaptogenesis restores benzodiazepine sensitivity in a mouse model of Status Epilepticus

Abstract

ABSTRACTPreviously we demonstrated that intra-hippocampal infusion of purified, Semaphorin 4D (Sema4D) extracellular domain into the mouse hippocampus rapidly promotes formation of GABAergic synapses and decreases seizure susceptibility in mice. Given the relatively fast action of Sema4D treatment revealed by these studies, we sought to determine the time course of Sema4D treatment on hippocampal network activity using an acute hippocampal slice preparation. We performed long-term extracellular recordings from area CA1 encompassing a 2 hour application of Sema4D and found that hippocampal excitation is suppressed hours following treatment. We also asked if Sema4D treatment could ameliorate seizures in an acute seizure model: the kainic acid (KA) mouse model of Status Epilepticus (SE). We demonstrate that Sema4D treatment suppresses seizures and lessens benzodiazepine (BZD) insensitivity which is a hallmark of refractory SE. Lastly, we sought to explore alternative methods of Sema4D delivery to hippocampus and thus created an Adeno Associated Virus expressing the extracellular domain of Sema4D. Our data reveal that virally delivered, chronically overexpressed Sema4D extracellular domain promotes GABAergic synapse formation and suppresses seizure activity similar to the actions of purified Sema4D protein. These results provide proof of concept that Sema4D-mediated GABAergic synapse development could combat BZD insensitivity in intractable forms of epilepsy, and that viral delivery of Sema4D is an efficacious and promising delivery method.